1. Field of the Invention
The present invention relates to a rubber composition with excellent workability that gives vulcanized products with high wet skid resistance, low rolling resistance and excellent abrasion resistance, and to a tire possessing treads produced from the rubber composition.
2. Description of the Prior Art
Recent requirements for lower fuel consumption by automobiles have led to demand for tire rubber materials that provide reduced tire rolling resistance. Tire rolling resistance can be reduced by lowering the low frequency energy loss of vulcanized rubber; tan xcex4 at 60xc2x0 C. is used as the evaluation index for vulcanized rubber, and starting rubber preferably has a small tan xcex4 at 60xc2x0 C.
Demands for running stability have made it highly desirable to provide starting rubber with high frictional resistance on wet surfaces (wet grip) and high frictional resistance on dry surfaces (dry grip). In order to increase the frictional resistance of tires on wet surfaces it is sufficient to increase the high frequency energy loss of vulcanized rubber; here, tan xcex4 at 0xc2x0 C. is used as the evaluation index for vulcanized rubber, and the starting rubber preferably has a large tan xcex4 at 0xc2x0 C.
However, the low rolling resistance and high frictional resistance on wet surfaces are in an antimonious relationship, and it has been very difficult to achieve both. The use of rubber compositions containing silica as a reinforcer instead of carbon black has been proposed in the past. Examples include rubber compositions comprising styrene-butadiene copolymer, vinylpolybutadiene and mixtures of silica and carbon black (Japanese Laid-open Patent Publication No. 252433 of 1991, No. 183868 of 1997, and the like.).
These methods, however, require the use of large amounts of expensive silane coupling agents in order to achieve an adequate effect, the mixing temperature must be controlled to no higher than 150-160xc2x0 C., and the workability of the compounded rubber prior to vulcanization is poorer.
It is an object of the present invention to provide a rubber composition with no mixing temperature problem and excellent workability prior to vulcanization, and which gives vulcanized products with high wet resistance and that satisfy both the required low rolling resistance and abrasion resistance.
It is another object of the invention to provide a tire with high wet skid resistance, low rolling resistance and excellent abrasion resistance.
According to the invention, the aforementioned objects are achieved by providing a rubber composition and tire with the composition described below.
[1] A rubber composition comprising a diene-based rubber (a), silica (b) at 5-100 parts by weight to 100 parts by weight of said diene-based rubber (a) and a compatibilizer (c) at 0.1-20 parts by weight to 100 parts by weight of said silica (b), characterized in that said compatibilizer (c) is at least one selected from among:
(I) Aminosilane compounds;
(II) Epoxy group-containing compounds;
(III) Compounds with an amino group and a hydroxyl group, an amino group and an epoxy group, an amino group and an ether, bond, an amino group and a carboxyl group, an amino group and an ester bond or an amino group and a polymerizable unsaturated bond in the molecule; and
(IV) Compounds with a polymerizable unsaturated bond and a hydroxyl group, a polymerizable unsaturated bond and an epoxy group, a polymerizable unsaturated bond and an ether bond, a polymerizable unsaturated bond and a carboxyl group or a polymerizable unsaturated bond and an ester bond in the molecule.
[2] A rubber composition comprising a diene-based rubber (a), silica (b) at 5-100 parts by weight to 100 parts by weight of said diene-based rubber (a) and a compatibilizer (c) at 0.1-20 parts by weight to 100 parts by weight of said silica (b), wherein said diene-based rubber (a) contains styrene-butadiene copolymer rubber at 30-100 wt % with respect to said diene-based rubber (a), and
said styrene-butadiene copolymer rubber has
(i) a styrene component content of 5-45 wt %;
(ii) a butadiene 1,2-bond content of 10-80 wt %;
(iii) a glass transition temperature of xe2x88x9270 to xe2x88x9210xc2x0 C.; and
(iv) an amino group content of 0.01-2.0 mmol per 100 g of said copolymer rubber, and
said compatibilizer (c) is at least one selected from among:
(I) Aminosilane compounds;
(II) Epoxy group-containing compounds;
(III) Compounds with an amino group and a hydroxyl group, an amino group and an epoxy group, an amino group and an ether bond, an amino group and a carboxyl group, an amino group and an ester bond or an amino group and a polymerizable unsaturated bond in the molecule;
(IV) Compounds with a polymerizable unsaturated bond and a hydroxyl group, a polymerizable unsaturated bond and an epoxy group, a polymerizable unsaturated bond and an ether bond, a polymerizable unsaturated bond and a carboxyl group or a polymerizable unsaturated bond and an ester bond in the molecule; and
(V) Ether bond-containing compounds.
[3] A rubber composition according to [2] above, wherein said compatibilizer (c) is at least one selected from among compounds of (I), (II), (III) and (IV) above.
[4] A rubber composition comprising a diene-based rubber (a), silica (b) at 5-100 parts by weight to 100 parts by weight of said diene-based rubber (a) and a compatibilizer (c) at 0.1-20 parts by weight to 100 parts by weight of said silica (b), wherein said diene-based rubber (a) contains styrene-butadiene copolymer rubber at 30-100 wt % with respect to said diene-based rubber (a), and
said styrene-butadiene copolymer rubber has
(i) a styrene component content of 5-45 wt %;
(ii) a butadiene 1,2-bond content of 10-80 wt %;
(iii) a glass transition temperature of xe2x88x9270 to xe2x88x9210xc2x0 C.; and
(iv) an alkoxysilyl group content of 0.01-5.0 mmol per 100 g of said copolymer rubber, and
said compatibilizer (c) is at least one selected from among:
(I) Aminosilane compounds;
(II) Epoxy group-containing compounds;
(III) Compounds with an amino group and a hydroxyl group, an amino group and an epoxy group, an amino group and an ether bond, an amino group and a carboxyl group, an amino group and an ester bond or an amino group and a polymerizable unsaturated bond in the molecule;
(IV) Compounds with a polymerizable unsaturated bond and a hydroxyl group, a polymerizable unsaturated bond and an epoxy group, a polymerizable unsaturated bond and an ether bond, a polymerizable unsaturated bond and a carboxyl group or a polymerizable unsaturated bond and an ester bond in the molecule; and
(V) Ether bond-containing compounds.
[5] A rubber composition according to [4] above, wherein said compatibilizer (c) is at least one selected from among compounds of (I), (II), (III) and (IV) above.
[6] A rubber composition comprising a diene-based rubber (a), silica (b) at 5-100 parts by weight to 100 parts by weight of said diene-based rubber (a) and a compatibilizer (c) at 0.1-20 parts by weight to 100 parts by weight of said silica (b), wherein said diene-based rubber (a) contains styrene-butadiene copolymer rubber at 30-100 wt % with respect to said diene-based rubber (a), and
said styrene-butadiene copolymer rubber has
(i) a styrene component content of 5-45 wt %;
(ii) a butadiene 1,2-bond content of 10-80 wt %;
(iii) a glass transition temperature of xe2x88x9270 to xe2x88x9210xc2x0 C.; and
(iv) an alkoxysilyl group content of 0.01-5.0 mmol and an amino group content of 0.01-2.0 mmol per 100 g of said copolymer rubber, and
said compatibilizer (c) is at least one selected from among:
(I) Aminosilane compounds;
(II) Epoxy group-containing compounds;
(III) Compounds with an amino group and a hydroxyl group, an amino group and an epoxy group, an amino group and an ether bond, an amino group and a carboxyl group, an amino group and an ester bond or an amino group and a polymerizable unsaturated bond in the molecule;
(IV) Compounds with a polymerizable unsaturated bond and a hydroxyl group, a polymerizable unsaturated bond and an epoxy group, a polymerizable unsaturated bond and an ether bond, a polymerizable unsaturated bond and a carboxyl group or a polymerizable unsaturated bond and an ester bond in the molecule; and
(V) Ether bond-containing compounds.
[7] A rubber composition according to [6] above, wherein said compatibilizer (c) is at least one selected from among compounds of (I), (II), (III) and (IV) above.
[8] A rubber composition according to any one of [1] through [7] above, which contains as a filler carbon black at 2-100 parts by weight to 100 parts by weight of said diene-based rubber (a).
[9] A tire characterized by possessing treads produced from a rubber composition according to [8] above.
[10] A tire characterized by possessing treads produced from a rubber composition according to any one of [1] through [7] above.
The rubber composition of the invention has excellent workability, as well as an excellent balance among abrasion resistance, wet skid properties and low rolling resistance. The features of the rubber composition of the invention can therefore be suitably used in applications for high performance tire and low fuel consumption tire treads and other tire applications, as well as for general purpose vulcanized rubber applications.
The tires possessing treads produced from the rubber composition of the invention have excellent abrasion resistance, wet skid properties and low rolling resistance and can therefore provide automobiles with low fuel consumption and excellent running stability.
The invention will now be explained in further detail.
The rubber composition of the invention contains a diene-based rubber (a) which may be, for example, styrene-butadiene copolymer rubber, acrylonitrile-styrene-butadiene copolymer rubber, butadiene rubber, isoprene rubber, butadiene-isoprene copolymer rubber, butadiene-styrene-isoprene copolymer rubber, natural rubber, acrylonitrile-butadiene copolymer rubber, chloroprene rubber or the like. These may be used alone or in combinations of two or more.
The Mooney viscosity (ML1+4, 100xc2x0 C.) of the diene-based rubber (a) is preferably 30-200, and more preferably. 40-150.
The diene-based rubber (a) is preferably used as an oil extended rubber, and the Mooney viscosity (ML1+4, 100xc2x0 C.) of the oil extended rubber is preferably 20-110, and more preferably 30-100.
The diene-based rubber (a) in the rubber composition of the invention preferably contains styrene-butadiene copolymer rubber at 30-100 wt %, and especially 50-100 wt %. The 3styrene-butadiene copolymer rubber also preferably satisfies the following conditions (i) to (iii) and any one of the conditions selected from the following conditions (iv-1)-(iv-3).
(i) A styrene component content of 5-45 wt %, and preferably 20-40 wt %.
(ii) A butadiene 1,2-bond content of 10-80 wt %, and preferably 15-75 wt %.
(iii) A glass transition temperature of xe2x88x9270 to xe2x88x9210xc2x0 C., and preferably xe2x88x9240 to xe2x88x9215xc2x0 C.
(iv-1) An amino group content of 0.01-2.0 mmol (preferably 0.1-1.5 mmol) per 100 g of the copolymer rubber.
(iv-2) An alkoxysilyl group content of 0.01-5.0 mmol (preferably 0.1-3.0 mmol) per 100 g of the copolymer rubber.
(iv-3) An alkoxysilyl group content of 0.01-5.0 mmol (preferably 0.1-3.0 mmol) and an amino group content of 0.01-2.0 mmol (preferably 0.1-1.5 mmol) per 100 g of the copolymer rubber.
Styrene-butadiene copolymer rubber satisfying these conditions can be manufactured by publicly known processes, and the following processes (a), (b) and (c) may be mentioned, though they are not restrictive.
(a) Alkoxysilyl Group-introduced Copolymer Rubber
This may be produced by copolymerizing styrene and 1,3-butadiene by anionic polymerization using an organic alkali metal compound such as n-butyllithium as the catalyst, and coupling the active alkali metal end of the resulting polymer with an alkoxysilane compound (for example, Japanese Laid-open Patent Publication No. 215701 of 1988).
(b) Amino Group-introduced Copolymer Rubber
This may be produced by copolymerizing styrene with 1,3-butadiene by anionic polymerization using an organic alkali metal compound such as n-butyllithium, in the presence of a primary or secondary amine, and preferably a secondary amine (for example, Japanese Laid-open Patent Publication No. 279515 of 1994).
(c) Alkoxysilane Group- and Amino Group-introduced Copolymer Rubber
Styrene-butadiene copolymer rubber with both alkoxysilyl groups and amino groups may be produced by bringing the process of (b) above to almost 100% conversion and then adding a modifier with alkoxysilyl groups.
Specific examples of the above-mentioned alkoxysilanes that may be used include the alkoxysilanes mentioned in, for example, Japanese Laid-open Patent Publication No. 233216 of 1995, of which there may be mentioned the following ones:
tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tetraphenoxysilane and tetratoluyloxysilane;
alkylalkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltributoxysilane, methyltriphenoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltripropoxysilane, ethyltributoxysilane, ethyltriphenoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldipropoxysilane, dimethyldibutoxysilane, dimethyldiphenoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, diethyldipropoxysilane, diethyldibutoxysilane and diethyldiphenoxysilane;
alkenylalkoxysilanes such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinyltributoxysilane, vinyltriphenoxysilane, allyltrimethoxysilane, octenyltrimethoxysilane, divinyldimethoxysilane and styryltrimethoxysilane;
arylalkoxysilanes such as phenyltrimethoxysilane, phenyltriethoxysilane, phenyltripropoxysilane, phenyltributoxysilane and phenyltriphenoxysilane;
halogenoalkoxysilanes such as trimethoxychlorosilane, triethoxychlorosilane, tripropoxychlorosilane, tributoxychlorosilane, triphenoxychlorosilane, dimethoxydichlorosilane, dipropoxydichlorosilane, diphenoxydichlorosilane, methoxytrichlorosilane, ethoxytrichlorosilane, propoxytrichlorosilane, phenoxytrichlorosilane, trimethoxybromosilane, triethoxybromosilane, tripropoxybromosilane, triphenoxybromosilane, dimethoxydibromosilane, diethoxydibromosilane, diphenoxydibromosilane, methoxytribromosilane, ethoxytribromosilane, propoxytribromosilane, phenoxytribromosilane, trimethoxyiodosilane, triethoxyiodosilane, tripropoxyiodosilane, triphenoxyiodosilane, dimethoxydiiodosilane, diethoxydiiodosilane, dipropoxyiodosilane, methoxytriiodosilane, ethoxytriiodosilane, propoxytriiodosilane and phenoxytriiodosilane;
halogenoalkylalkoxysilanes such as xcex2-chloroethylmethyldimethoxysilane and xcex3-chloropropylmethyldimethoxysilane; and
nitroalkylalkoxysilanes such as xcex2-nitroethylmethyldimethoxysilane and xcex3-nitropropylmethyldimethoxysilane.
As examples of the above-mentioned secondary amines there may be mentioned aliphatic secondary amines, aromatic secondary amines and cyclic imines, among which aliphatic secondary amines and cyclic imines are preferred.
As examples of aliphatic secondary amines there may be mentioned dimethylamine, methylethylamine, methylpropylamine, methylbutylamine, methylamylamine, amylhexylamine, diethylamine, ethylpropylamine, ethylbutylamine, ethylhexylamine, dipropylamine, diisopropylamine, propylbutylamine, dibutylamine, diamylamine, dihexylamine, diheptylamine, dioctylamine, methylcyclopentylamine, ethylcyclopentylamine, methylcyclohexylamine, dicyclopentylamine and dicyclohexylamine. Preferred among these are dimethylamine, methylethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, diamylamine, dihexylamine, diheptylamine and dioctylamine.
As examples of aromatic secondary amines there may be mentioned diphenylamine, N-methylaniline, N-ethylaniline, dibenzylamine, N-methylbenzylamine and N-ethylphenethylamine.
As examples of cyclic imine compounds there may be mentioned aziridine, acetidin, pyrrolidine, piperidine, 2-methylpiperidine, 3-methylpiperidine, 4-methylpiperidine, 3,5-ddimethylpiperidine, 2-ethylpiperidine, hexamethyleneimine, heptamethyleneimine, dodecamethyleneimine, coniine, morpholine, oxazine, pyrroline, pyrrole and azepine. Preferred among these are pyrrolidine, piperidine, 3-methylpiperidine, 4-methylpiperidine, 3,5-dimethylpiperidine, 2-ethylpiperidine, hexamethyleneimine and heptamethyleneimine.
These secondary amine compounds may be used alone or in combinations of two or more.
The butadiene 1,2-bond content mentioned in (ii) above can be adjusted to the aforementioned ranges by using an ether compound or tertiary amine as a bond adjustor.
As examples of the aforementioned ether compounds or tertiary amines there may be mentioned dimethoxybenzene, tetrahydrofuran, dimethoxyethane, diethyleneglycol dibutylether, diethyleneglycol dimethylether, triethylamine, pyridine, N-methylmorpholine, N,Nxe2x80x2,Nxe2x80x2-tetramethylethylenediamine and dipiperidinoethane.
The glass transition temperature mentioned in (iii) above can be adjusted by the styrene content and the 1,2-bond (vinyl) content in the microstructure of the butadiene portion. The relationship is such that increasing the styrene content and the 1,2-bond (vinyl) content in the microstructure of the butadiene portion produces a higher glass transition temperature.
This relationship can be used to adjust the glass transition temperature to the above-mentioned range by, for example, a method in which the charging amount of the styrene during polymerization is controlled to adjust the styrene content, a method in which the amount of polar compound added, such as the ether compound or tertiary amine, is controlled during polymerization to adjust the 1,2-bond (vinyl) content (increasing the amount of polar compound added increases the 1,2-bond (vinyl) content), or a combination of these methods. A polar compound or potassium dodecylbenzenesulfonate, potassium linoleate, potassium benzoate, potassium phthalate or potassium tetradecylbenzenesulfonate can also serve as styrene randomizers.
The rubber composition of the invention also contains silica (b) as a filler which is not particularly restricted and may be any precipitated silica, dried silica or synthetic silicate-based silica. A higher reinforcing effect is provided by silica with a small particle size, and small particulate/high aggregate types (high surface area, high oil absorption) have satisfactory dispersability in rubber and are therefore particularly preferred from the standpoints of physical properties and workability.
The mean particle size of the silica (b) is preferably 5-60 xcexcm and especially 8-40 xcexcm, as the primary particle size.
The content of the silica (b) is 5-100 parts by weight, and more preferably 10-90 parts by weight, to 100 parts by weight of the diene-based rubber (a).
In the rubber composition of the invention, carbon black and the silica (b) are preferably used together as fillers, in which case the carbon black is preferably added at 2-100 parts by weight to 100 parts by weight of the diene-based rubber (a) and the silica (b) added at 5-100 parts by weight to 100 parts by weight of the diene-based rubber (a).
The rubber composition of the invention may also contain as additional fillers, carbon-silica dual phase filler, clay, calcium carbonate, magnesium carbonate and the like, in amounts selected as necessary.
For the diene-based rubber (a) as stated in claim 1, the compatibilizer (c) may be at least one compound selected from among (I) to (IV) below. For the diene-based rubber (a) as stated in any one of claims 2, 4 and 6, the compatibilizer (c) may be at least one compound selected from among (I) to (V) below, and it is more preferably at least one compound selected from among (I) to (IV) below.
As specific examples of the xe2x80x9c(I) aminosilane compoundsxe2x80x9d there may be mentioned hexamethyldisilazane, nonamethyltrisilazane, anilitrimethylsilane, bis(dimethylamino)dimethylsilane, bis(diethylamino)dimethylsilane and triethylaminosilane. Preferred among these are silazane compounds and bis(dimethylamino)dimethylsilane.
As specific examples of the xe2x80x9c(II) epoxy group-containing compoundsxe2x80x9d there may be mentioned butylglycidylether, diglycidylether, propylene oxide, neopentylglycol diglycidylether, epoxy resins, epoxidized soybean oil and epoxidized fatty acid esters.
As specific examples of the xe2x80x9c(III) compounds with an amino group and a hydroxyl group, an amino group and an epoxy group, an amino group and an ether bond, an amino group and a carboxyl group, an amino group and an ester bond or an amino group and a polymerizable unsaturated bond in the moleculexe2x80x9d there may be mentioned the following:
[1] Compounds with an amino group and a hydroxyl group in the molecule: trimethylbenzylammonium hydroxide, gamma acids, triethanolamine, diethanolamine, triisopropanolamine, diisopropanolamine, aminophenol, trans-1,2-cyclohexanediamine tetraacetate, 3-amino-1-propanol, N-methylethanolamine, N,N-dibutylethanolamine, N-methyldiethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, pyridinemethanol, p-hydroxyphenylacetamide, and the like.
[3] Compounds with an amino group and an epoxy group in the molecule: N,N-diglycidyl-o-toluidine, polyglycidylamine, N,N-diglycidylaniline, N,N-diglycidyl-o-toluidine, tris-epoxypropylisocyanurate, and the like.
[3] Compounds with an amino group and an ether group in the molecule: diaminodiphenylether, morpholine, N-(3-aminopropyl)morpholine, 2-methyl-4-methoxydiphenylamine, p-phenetidine, p-cresidine, 3-isopropoxyaniline, 3-lauryloxypropylamine, and the like.
[4] Compounds with an amino group and a carboxyl group in the molecule: anthranilic acid, sodium phthalaminate, p-aminobenzoic acid, iminodiacetic acid, aminododecanoic acid, aminocarboxylates, carboxybetaine, imidazoliniumbetaine, pyradinemonocarboxylic acid, 2,3-pyrazinedicarboxylic acid, picolinic acid, citrazinic acid, keridamu acid, quinaldic acid, 3-carbamoyl-pyrazinecarboxylic acid, xe2x80x9cKENGARDxe2x80x9d (trade name of Kenko Tsusho Co.), and the like.
[5] Compounds with an amino group and an ester group in the molecule: ethyl p-aminobenzoate, polyurethane, methyl polyglutamate, and the like.
[6] Compounds with an amino group and a polymerizable unsaturated bond in the molecule: 4,4xe2x80x2-diaminostilbene-2,2xe2x80x2-disulfonic acid, diacetoneacrylamide, N-[3-(dimethylamino)propyl]methacrylamide, N-t-octylacrylamide, diallylamine, 2-vinylpyridine, triacrylformalate, triallyl isocyanurate, 2-acrylamido-2-methylpropanesulfonic acid, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, and the like.
As specific examples of the xe2x80x9c(IV) compounds with a polymerizable unsaturated bond and a hydroxyl group, a polymerizable unsaturated bond and an epoxy group, a polymerizable unsaturated bond and an ether bond, a polymerizable unsaturated bond and a carboxyl group or a polymerizable unsaturated bond and an ester bond in the moleculexe2x80x9d there may be mentioned the following:
[1] Compounds with a polymerizable unsaturated bond and a hydroxyl group in the molecule: allyl alcohol, polyoxyethylenenonyl propenylphenyl ether, polyoxyethyleneallylglycidyl nonylphenyl ether, bisabolol, hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, and the like.
[2] Compounds with a polymerizable unsaturated bond and an epoxy group in the molecule: epoxidized soybean oil, epoxidized coconut oil, epoxidized palm oil, glycidyl methacrylate, and the like.
[3] Compounds with a polymerizable unsaturated bond and an ether bond in the molecule: trimethylolpropane diallylether, diethyleneglycol bisallylcarbonate, tetrahydrofurfuryl methacrylate, and the like.
[4] Compounds with a polymerizable unsaturated bond and a carboxyl group in the molecule: dodecadienic diacid, crotonic acid, itaconic acid, oleic acid, 2-methacryloyloxyethylsuccinic acid, and the like.
[5] Compounds with a polymerizable unsaturated bond and an ester bond in the molecule: cyclohexyl acrylate, allyl acetate, diethyl ethoxymethylenemalonate, diallyl terephthalate, diallyl isophthalate, isobutyl acrylate, tripropyleneglycol acrylate, tetraethyleneglycol acrylate, 2-methoxyethyl acrylate, lauryl acrylate, n-stearyl acrylate, trimethylolpropane triacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, pentaerythritol triacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, alkyl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, and the like.
As specific examples of the xe2x80x9c(V) ether bond-containing compoundsxe2x80x9d there may be mentioned isopropyl ether and dibutyl ether.
The content of the compatibilizer (c) is preferably 0.1-20 parts by weight and more preferably 0.5-10 parts by weight, to 100 parts by weight of the silica (b) added.
The rubber composition of the invention may also contain vulcanizing agents, vulcanization accelerators, extender oils or other additives if desired.
A typical vulcanizing agent that is used is sulfur, and sulfur-containing compounds, peroxides and the like may also be used. The amount of vulcanizing agent to be used is normally 0.5-10 parts by weight and preferably 1-6 parts by weight, to 100 parts by weight of the diene-based rubber (a).
Vulcanization accelerators include aldehydeammonia-based, guanidine-based, thiourea-based, thiazole-based and dithiocarbaminic acid-based compounds. The amount of vulcanization accelerator to be used is normally 0.5-15 parts by weight and preferably 1-10 parts by weight, to 100 parts by weight of the diene-based rubber (a).
As extender oils there may be mentioned petroleum-based compounded oils such as aromatic process oils, naphthene-based process oils and paraffin-based process oils, with aromatic process oils and naphthene-based process oils being preferred. The amount of extender oil to be used is normally 0-100 parts by weight and preferably 5-50 parts by weight, to 100 parts by weight of the diene-based rubber (a).
Other additives that may be used as desired or as necessary include silane coupling agents, zinc oxide, vulcanizing aids, antioxidants, processing aids and the like.
When preparing the rubber composition of the invention, first the diene-based rubber (a), compatibilizer (c), silica (b), the other fillers (carbon black, carbon-silica dual phase filler, and the like), the extender oil and other additives are blended at a temperature of 70-180xc2x0 C. using a kneading machine such as a Banbury mixer. Next, the resulting mixture is cooled and then the vulcanizing agent such as sulfur and the vulcanization accelerator, and the like are blended therewith using a Banbury mixer or mixing roll, to prepare a rubber composition. The prepared rubber composition is molded into the desired shape and vulcanized at a temperature of 140-180xc2x0 C. to produce vulcanized rubber of the desired shape, i.e. the rubber product.
The vulcanized rubber composition of the invention has an excellent balance between abrasion resistance, wet skid properties and low rolling resistance, and therefore is suitable to be used for high performance tire and low fuel consumption tire treads.
Tires possessing treads produced from the rubber composition of the invention exhibit excellent abrasion resistance, wet skid properties and rolling resistance, and automobiles using the tires exhibit low fuel consumption and excellent running stability.
The present invention will now be explained in greater detail by way of examples which, however, are in no way intended to restrict the scope of the invention. Throughout, styrene-butadiene copolymer rubber will be referred to as xe2x80x9ccopolymer rubberxe2x80x9d.
The compatibilizers used in the examples were the following.
Compatibilizer xe2x80x9caxe2x80x9d: Dibutylether, product of Wako Junyaku
Compatibilizer xe2x80x9cbxe2x80x9d: Hexamethyldisilazane, product of Shinetsu Chemicals, KK.
Compatibilizer xe2x80x9ccxe2x80x9d: xe2x80x9cEpoxidized Soybean Oil SOxe2x80x9d, trade name of Daihachi Chemical Industries, KK.
Compatibilizer xe2x80x9cdxe2x80x9d: 3-Lauryloxypropylamine, product of Wako Junyaku
Compatibilizer xe2x80x9cexe2x80x9d: Triethanolamine, product of Wako Junyaku
Compatibilizer xe2x80x9cfxe2x80x9d: 2-Methacryloyloxyethyl succinate, product of Kyoeisha Chemical Co.
Compatibilizer xe2x80x9cgxe2x80x9d: xe2x80x9cKENGARD 300-Pxe2x80x9d, trade name of Kenko Tsusho
Compatibilizer xe2x80x9chxe2x80x9d: xe2x80x9cStruktol EF44xe2x80x9d, trade name of SCHILL AND SEILACHER, mixture of fatty acid salt and fatty acid.
The various measurements for the examples were conducted according to the following methods.
(1) Content of Vinyl in Butadiene Portion (%)
Determined by the infrared absorption spectrum method (Morello method).
(2) Content of Bonded Styrene (%)
Determined by the infrared absorption spectrum method, based on a calibration curve.
(3) Mooney Viscosity (ML1+4, 100xc2x0 C.)
Measured according to JIS K6300 with an L-rotor, 1 minute preheating, 4 minute rotor operation time, and a temperature of 100xc2x0 C.
(4) Content of Alkoxysilyl Group (mmol/100 g Rubber)
This was quantified based on a calibration curve prepared for absorption near 1160 cmxe2x88x921 due to Sixe2x80x94C bonds in an infrared absorption spectrum. The measured value was divided by the number average molecular weight(Mn) in terms of polystyrene obtained by the GPC method and the alkoxysilyl group molecular weight to obtain the number of moles of alkoxysilyl groups.
(5) Content of Amino Group (mmol/100 g Rubber)
This was measured and determined according to the following method based on the xe2x80x9cAcid-base titration method using perchloric acid-acetic acid solutionxe2x80x9d described in J. Anal. Chem., Vol.24, p.564 (1952) by Robert T. Keen and James S. Fritz. Chloroform was used as the solvent for dissolution of the sample, Methyl Violet was used as the titration indicator, and the amino group content was quantified based on a calibration curve prepared from a tri-n-octylamine solution of known concentration.
(6) Glass Transition Temperature (xc2x0C.)
A differential scanning calorimeter (DSC) by Seiko Denshi Kogyo, KK. was used for measurement at a temperature increase rate of 10xc2x0 C./min, and the extrapolation initiation temperature was recorded as the glass transition temperature.
(7) Molecular Weight Distribution (Mw/Mn)
Gel permeation chromatography (GPC) was used to determine the distribution in terms of polystyrene.
(8) Property Evaluation of Vulcanized Product
The starting rubber was mixed in a 1.7 liter Banbury mixer kneading machine according to one of the formulations T-Z listed in Table 2, and then vulcanization was carried out for a prescribed time at 145xc2x0 C. and the vulcanized product was subjected to various measurements.
(a) tan xcex4 (60xc2x0 C.) and tan xcex4 (0xc2x0 C.)
A dynamic spectrometer by U.S. Rheometrix was used.
The conditions for measurement of tan xcex4 (60xc2x0 C.) were 1% tension distortion, a frequency of 10 Hz and a temperature of 60xc2x0 C. The measurement results are expressed as the measured value, with a smaller value indicating lower (more satisfactory) rolling resistance.
The same instrument was used for measurement of tan xcex4 (0xc2x0 C.), with 0.1% tension distortion, a frequency of 10 Hz and a temperature of 0xc2x0 C. The measurement results are expressed as the measured value, with a larger value indicating greater (more satisfactory) wet skid resistance.
(b) Lamborn Abrasion Factor
A Lamborn abrasion test machine was used, the factor was expressed as the degree of abrasion for a 60% slip rate, and the measuring temperature was room temperature. A larger factor indicates more satisfactory abrasion resistance.
(c) Workability
After mixing, the Mooney viscosity (ML1+4, 100xc2x0 C.) of the compounded rubber was evaluated.
(d) Hardness
This was measured using a JIS hardness meter Type (A), at a temperature of 25xc2x0 C.